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 Post subject: Forecast for the Upcoming Snow Season
Post Posted: Sep 11, 2015 7:38 am 
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Forecast for the 2015-2016 Snowfall Season - posted September 11, 2015

I thought I would post some information on the current El Nino in the Pacific, and provide some historical insights into what our upcoming snow season may be like, based on past events.

First a little background. The El Nino Southern Oscillation (ENSO) is a cyclical phenomenon of warmer than average sea sruface temperatures in the Pacific Ocean that move back and forth between the western Pacific and eastern Pacific. A warm episode of ENSO is referred to as El Nino conditions wnen warmer than average sea surface temperatures move into the eastern equatorial Pacific. Conversely, a cool episoide is referred to as La Nina conditions when cooler than average sea surface temperatures moves into the eastern equatorial Pacific. The term El Nino originated in Peru and Equador, when the warmer than average sea surface temperaturs often peak in December, the local fisherman would find fishing difficult due to the wamer waters, and referenced the phenomenon as El Nino - The Christ Child, due to the proximity to Christmas. We have been taking sea surface measurements since 1950, so that is as far back as records exist. A link to the Climate Prediction Center ENSO site is here: http://www.cpc.ncep.noaa.gov/products/p ... enso.shtml

The past 2 years have seen Nuetral ENSO conditions. Now, we are on the verge of a historical El Nino event. The Oceanic Nino Index (ONI) measures the sea surface temperature anomoly, or departures from average. When the ONI is between +0.5 and -0.5, we have Nuetral Conditions. When the ONI is from 0.5 to 1.0, we have weak El Nino conditions. When the ONI is from 1.0 to 1.5, we have moderate El Nino conditions, and when the ONI is above 1.5, we have strong El Nino conditions. The converse is true for La Nina conditions, just with values less than zero. The ONI is measured in different ways. We get weekly ONI values as well as a 3 month mean value. El Nino is generally referenced using the 3 month mean value.

Since 1950, we have observed 5 strong El Nino events, 1957/1958, 1972/1973, 1982/1983, 1987/1988, and 1997/1998. Currently, the weekly ONI value is 2.1, while the last 3 month mean value for June-August is 1.2. All models predict the current El Nino to further strengthen into the coming winter, with an expected 3 month mean value above 2.0. Of the 5 referenced strong El Nino events, 3 have had a 3 month ONI above 2.0, which was 1972/73 (2.0), 1982/83(2.1), and 1997/98 (2.3). If we use these past events to look at snowfall across CO, we can get a picture of what may happen this year.

We only have snowfall records for the foothills since 1993, so a limited historical perspective, but we can use Denver snowfall records for earlier events. in 1972/73, Denver received 94.9 inches of snow, well above the average of 57 inches. In 1982/83, Denver received 81.6 inches of snow, also well above average. In 1997/98, Denver received 72.1 inches, while Conifer Mountain received 255.5 inches, which is well above the average of 170 inches on Conifer Mountain. We have also seen when there is a moderate El Nino, snowfall tends to be avove average in both Denver and the foothills. The same is not true west of the Divide. Many times, El Nino conditions result in below average snowfall for mountain areas of CO. Specific to the foothills, every time since 1993 there has been a moderate or strong El Nino, snowfall has been above average. In Denver, 93% of years with a moderate or strong El Nino, snowfall has been above average. Thus, using past records, it is very likely eastern CO will see above average snowfall this coming season. Usually, Conifer Mountan will see more than 200 inches of snow during such events. Moderate to strong El Nino events also have impacts across the entire U.S. Above average precipitation become likely from central and southern CA across AZ, NM, TX and the Gulf Coast states into the Southeast U.S. Below average precipitation is more likely across the Pacific Northwest, northern tier states and into the Great Lakes and New England. In general, El Nino episodes feature a strong zonal (west to east) jetstream across the northern Pacific that brings strong Pacific storms into CA and moves that moisture along the southern U.S. In CO, we tend to see an increase in upper level lows that form to our south creating good upslope snow events across eastern CO. We tend to see an increase in these events beginning in October. El Nino years tend to feature some very heavy storms, where eastern CO areas can receive 2-4 feet of snow from individual storms. Snow can sometimes fade during winter months, but strong Spring storms often acompany El Nino events. The past 2 strongest El Nino episodes for us were 1997/98 and 2009/10. In 1997/98, Conifer Mountain had 44 inches of snow in October, and we had 50 inches in October of 2009. Spring of each of those seasons also had months with over 50 inches of snow.

Now the caviat. Every El Nino is different, how it evolves, when it peaks and how fast it fades all tie into the potential weather. We think we know how this current El Nino will evolve, but that is still a forecast. If I were to make a guess, I would guess that snowfall on Conifer Mountain this season will be from 210-240 inches, well above our average of 170 inches. So, time to prepare for a heavy snow season for eastern CO. For skiers, we could see a decent start to the season, but overall snow is likely to be below average for most resorts, especially those farther north and west.

--------------------- What Actually Happened --------------------------------------------------

Validation - The ONI during winter months was a whopping 2.3 which created one of the strongest El Nino seasons since records began in 1950. As expected this created above average snowfall across most of CO, especially eastern CO and a very snowy Spring.

Snowfall on Conifer Mountain - 225.0 inches (161.5)
Days with snow - 65 (59.7)
Days with 2.0 inches of snow or more - 37 (26.5)
Number of storms with greater than 12 inches - 7 (3.7)

_________________
"Climatology is what you expect, Weather is what you get" - R. Heinlein.

"Sunshine is delicious, rain is refreshing, wind braces us up, snow is exhilarating; there is really no such thing as bad weather, only different kinds of good weather" - John Ruskin


Last edited by wxgeek on May 23, 2018 12:38 pm, edited 3 times in total.

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 Post subject: Re: Forecast for the Upcoming Snow Season
Post Posted: Aug 30, 2016 2:29 pm 
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Forecast for the 2016-2017 snowfall season - posted August 30 2016

As expected, we have transitioned from a very strong El Nino in 2015-2016 to ENSO Neutral conditions this summer, and we are forecast to move into a weak to moderate La Nina by this Fall and Winter. For every strong El Nino since 1950, the following season has been a moderate to strong La Nina, and thus we should expect the same to happen this year. The Oceanic Nino Index (ONI) is currently at -0.5, which is on the verge of weak La Nina conditions. As Fall arrives and progresses into Winter, the ONI is expected to range from -0.5 to -1.5, which would be a weak to moderate La Nina. Using past climate information, here is what we should expect for the coming snow season in Colorado.

Since 1993, when snowfall records began on Conifer Mountain, we have had 9 seasons with La Nina conditions. 3 of those seasons had above average snowfall, while 6 of them had below average snowfall. Average snowfall during all La Nina seasons is 151.7 inches, or 86% of our average snowfall of 174 inches. Of the 9 La Nina seasons, 5 of them have been categorized as "weak" La Nina episodes. Of these 5 weak La Nina seasons, 4 have been below average snowfall and 1 was above average. The average snowfall was 143 inches, or 82% of average. 4 of the past 9 La Nina seasons have been categorized as "strong" La Nina episodes. Of these 4, 2 had above average snowfall and 2 had below average snowfall, with an average of 163 inches, or 93% of average.

Thus, the probability for our upcoming snow season favors below average snowfall for the foothills, as well as for the Urban Corridor and eastern plains. The only locations in Colorado that get above average snowfall is the central and northern mountains during La Nina seasons. The stronger the La Nina, the higher our snowfall tends to be. If we have a weak La Nina season, probability is 80% for below average snowfall, while a strong La Nina poses a 50% probability for below average snowfall. In addition, La Nina seasons tend to favor more episodes of strong downslope or "Chinook" winds east of the Divide. Temperatures tend to be mostly above average across eastern CO during La Nina episodes, but we have a higher probability of more arctic outbreaks during a La Nina season, so we may see some very cold spells from December into February. The jetstream tends to migrate farther north during La Nina seasons, so the Pacific Northwest favors wetter than average precipitation, while CA and the Desert Southwest tend to be drier than average.

During most of our past La Nina seasons, the Fall can be close to above average snowfall with October and November being colder and snowier than average. Then the winter months tend to be warmer and drier than average from December through February, and the drier and warmer pattern persists into Spring, which tends to be our snowiest time of year. This can cause an early fire season across much of eastern CO.

So, my prediction for the upcoming snow season is from 140-170 inches of snow on Conifer Mountain, which is from 80-97% of average.

---------------------- What Actually Happened ------------------------------

Validation - The ONI during winter months was -0.8, so a weak La Nina ensued, creating dry conditions across most of eastern CO and near average snowfall along and west of the Divide. Every month from September through March had below average snowfall. It was not until April that we received above average snowfall that continued into May. Here are the stats with averages in parentheses:

Snowfall on Conifer Mountain - 123.5 inches (161.5)
Days with snow - 50 (59.7)
Days with 2.0 inches of snow or more - 21 (26.5)
Number of storms with greater than 12 inches - 3 (3.7)

_________________
"Climatology is what you expect, Weather is what you get" - R. Heinlein.

"Sunshine is delicious, rain is refreshing, wind braces us up, snow is exhilarating; there is really no such thing as bad weather, only different kinds of good weather" - John Ruskin


Last edited by wxgeek on May 23, 2018 12:36 pm, edited 2 times in total.

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 Post subject: Re: Forecast for the Upcoming Snow Season
Post Posted: Sep 15, 2017 12:59 pm 
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Forecast for the 2017-2018 Snow Season

After a brief warming period in the tropical eastern Pacific this Spring, waters have cooled into ENSO Neutral conditions, and over the past month have trended towards weak La Nina conditions. Most of the models suggest ENSO conditions will remain from Neutral to weak La Nina during the coming Fall and Winter seasons.

So what does that mean for our upcoming snowfall season you may ask, well, the forecast from last year will suit this coming season very closely. In our foothills, we tend to have below average snowfall with either ENSO Neutral or La Nina conditions. Weak La Nina conditions pose an 80% probability of below average snowfall, while ENSO Neutral conditions have a 67% probability of having below average snowfall on Conifer Mountain. Blending, I would give us a 75% probability of having below average snowfall this coming season. There is the 25% chance we could see average to slightly above average snowfall.

For the coming Fall season, it looks like we could have very dry and warm conditions. This is based on the latest MJO pattern, which would keep us dry the next 30-60 days before a more favorable positive MJO pattern would move towards CO. Thus, we could see late fire season activity in September and October, possibly into early November. Perhaps we may see a more active cycle in mid to late November into December, then a drier pattern January into February, with the potential as is usually the case a more active Spring season. If the La Nina pattern strengthens, the the likelihood of a drier season may increase. Now for the forecast:

For the foothills and eastern plains, I expect below average snowfall, and for temps to be warmer than average with downslope Chinnok winds to be stronger than average. In the mountains, I would expect below average snowfall in the Southwest and South Central mountains, while average to slightly above average snowfall in the Cental and Northern Mountains, with heaviest snow expected in the Northern Mountains. For Conifer Mountain, my snowfall prediction is 125-150 inches for the coming season.

------------------ What Actually Happened ------------------------

As predicted, this season was a typical La Nina year, with the 3 month ENSO ONI reaching -1.0 making this on the border between a weak and moderate La Nina. CO weather was highlighted by above average temperatures and windy conditions for much of the winter season. Even mountain areas suffered from below average snowfall, and from the foothills east we saw well below average snowfall. This wa sthe first season since 1993 in which not one month had more than 16 inches of snowfall. Here are the stats from the year, numbers in parenthesis are averages:

Snowfall on Conifer Mountain - 101.5 inches (161.5)
Days with snow - 35 (59.7)
Days with 2.0 inches of snow or more - 20 (26.5)
Number of storms with greater than 12 inches - 0 (3.7)

_________________
"Climatology is what you expect, Weather is what you get" - R. Heinlein.

"Sunshine is delicious, rain is refreshing, wind braces us up, snow is exhilarating; there is really no such thing as bad weather, only different kinds of good weather" - John Ruskin


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 Post subject: Re: Forecast for the Upcoming Snow Season
Post Posted: Sep 20, 2018 1:12 pm 
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Forecast for the 2018-2019 Snow Season

After two very dry seasons, we are ready for more snowfall, and it appears Mother Nature may cooperate this coming season. A weak to moderate El Nino is currently building in the eastern Pacific ocean. Although current El Nino Southern Oscillation (ENSO) conditions remain Neutral (0.3) the trend and forecast is for conditions to become a weak to possibly moderate El Nino by November and persist into Spring of 2019. Model consensus has the ENSO between 0.8 and 1.2 for the coming season which should bode well for most of eastern Colorado. In the foothills, we have seen 4 weak to moderate El Nino seasons since 1993 when records began. The average snowfall for these 4 seasons is 221.5 inches, which is well above our average of 170 inches. Record snowfall from 2006/2007 tends to raise the average for this, but there are some similarities from an ENSO standpoint between 2006/2007 and this coming season, but every season is different. So far, there has never been below average snowfall on Conifer Mountain during any EL Nino episode, I certainly hope that remains true after this season.

That said, my prediction for the upcoming snow season on Conifer Mountain is between 180 and 220 inches.

In typical EL Nino seasons we can receive some big storms in the Fall as well as in Spring months as well as in Winter. El Nino seasons tend to have fewer Downslope High Wind events, and also fewer Arctic Air outbreaks into Colorado, but with more snowy days and sometimes mild temperatures. Most of eastern Colorado tends to have above average snowfall from the Continental Divide east. As for areas along and west of the Continental Divide, it can be a mixed bag for snow. Some El Nino seasons have been very dry for the mountains, while other seasons can provide big snow for southwest CO and near to below average snow for the central and northern mountains.

_________________
"Climatology is what you expect, Weather is what you get" - R. Heinlein.

"Sunshine is delicious, rain is refreshing, wind braces us up, snow is exhilarating; there is really no such thing as bad weather, only different kinds of good weather" - John Ruskin


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